Background

The family Scorpaenidae represents a large array of fish characterized by the ability to envenomate with various types of specialized spines. This group of fish is responsible for the second most common piscine envenomation, after stingrays.

Unfortunately, this family of fish has a confusing variety of common names, which tends to hinder accurate field identification, classification, and understanding of envenomation. It is helpful to consider the Scorpaenidae family as three distinct groups, based upon their venom organ structure and toxicity.

These three groups and their representative genera include the following (see the images below):

Pathophysiology

Common to the family Scorpaenidae are 12-13 dorsal spines, two pelvic spines, and three anal spines. Each spine is associated with a pair of venom glands. A loose integumentary sheath covers each spine. The sheath is pushed down the spine during envenomation, causing compression of the venom glands located at the base of the spines. Venom then travels from the glands through anterolateral depressions in the spines and into the wound, in a manner analogous to that of a stingray envenomation. The pectoral spines, while often ornate and plumelike, are innocuous. The venom toxicity is due to antigenic, heat-labile proteins of high molecular weight. Treatment is based on the proposed heat-labile characteristics of these proteins.

Epidemiology

United States

The true number of Scorpaenidae envenomations is unknown. However, there are more than 100 reported cases of captive lionfish (genus Pterois) envenomations in the medical literature, nearly all of which occur on the hands of unwary marine aquarists. Reports from coastal locales commonly involve fisherman, divers, and other water enthusiasts who inadvertently may step on or carelessly handle members of the Scorpaenidae family.

International

This large family is widespread throughout the tropical, subtropical, and temperate regions. Some species are even found in polar regions. No accurate estimates regarding the international frequency of Scorpaenidae envenomations are available; however, they are not uncommon. While the tropical seas contain the majority of species, the temperate waters of the Indo-Pacific, India, South Africa, Australia, Philippines, China, Japan, and the United States are home to many venomous Scorpaenidae.

Prognosis

The severity of Scorpaenidae envenomations is progressively worse from Pterois to Scorpaena to Synanceia species.

Pterois (eg, lionfish, zebrafish, turkey fish, butterfly cod): In one series of 101 described cases of captive lionfish (genus Pterois) envenomations in the United States, 92% of patients experienced local pain, 60% experienced edema, and 13% experienced systemic symptoms. There were no fatalities. Wounds were graded with the use of a grading system, and 95% of the wounds were found to be grade I (erythema), 4% were found to be grade II (vesicle formation), and 1% were found to be grade III (tissue necrosis). Pain was relieved with hot-water immersion therapy in 97% of the patients, and 0% of the patients required antivenom administration. One patient required intravenous antibiotics, one hypotensive patient responded well to intravenous fluids, and 13% of patients had variable, less severe, systemic symptoms.

Judging from this and other reports in the United States, the vast majority of lionfish stings appear to result in uncomplicated wounds with severe local pain that is responsive to immersion therapy. While reports of fatalities exist, detailed documentation is sparse and deaths must be very rare.

Scorpaena (eg, scorpionfish, bullrout, sculpin) and Synanceia (eg, stonefish, warty-ghoul, "nofu"): Wound severity and systemic symptoms are generally accepted to be greater in Scorpaena and Synanceia envenomations as compared to Pterois envenomations. Of some controversy is the purported lethality of these envenomations. Fenner and Williamson note the absence of any well-documented Australian fatalities or life-threatening symptoms and go on to cite only three specific references in the literature of death attributable to envenomation by stonefish.[1] One of these cases (Mozambique, 1957) was postulated to represent direct intravascular deposition of venom or, perhaps, anaphylaxis, as the victim's foot showed no local reaction.

Other reports describe deaths occurring days or months following envenomation, raising suspicion of secondary complications (eg, wound infection, tetanus). Whatever the actual mortality rate is following a stonefish envenomation, the number of confirmed human deaths is much fewer than commonly believed. Nonetheless, severe and incapacitating local and systemic effects are well described.

Physical Examination

The severity of envenomation depends upon multiple factors including the offending species, the number of stings, and the age and underlying health of the victim. Scorpaenidae stings are progressively more severe from Pterois (lionfish) to Scorpaena (scorpionfish) to Synanceia (stonefish).

Puncture wound

See the image below.

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A 45-year-old diver was taking photographs in Australia at a depth of 60 feet. He suddenly noticed an excruciating pain in his left foot after resting....

Classic envenomation reveals one or more puncture wounds, each discolored by a surrounding ring of bluish cyanotic tissue.

Subsequent edema, erythema, and warmth may involve the entire limb, although it rarely results in tissue necrosis in the absence of secondary infection (in marked contrast to stingray envenomation injuries).

Vesicle formation, particularly of the hands, may be followed by rapid tissue sloughing, cellulitis, and surrounding hypesthesia.

Imaging Studies

Plain film radiography

Soft tissue radiographs are advised as the initial study modality when attempting to exclude retained foreign bodies. Most calcareous spines are visualized directly or indirectly with the use of plain radiographs.

Nonradiodense objects may be revealed as filling defects, or they may be outlined by air drawn into the wound during injury.

Ultrasound

If an object cannot be visualized by plain film radiography or retrieved easily through direct visualization, ultrasound may be used.

Ultrasound can detect nonradiodense foreign bodies as small as 1 mm by 2 mm, and it can be used to accurately localize foreign material and provide guidance during removal.

Prehospital Care

Prehospital care should address recognition of the injury as a potential envenomation, gentle removal of visible spines, direct pressure to control bleeding, administration of analgesia, and transport for definitive medical evaluation.

Recognition of serious systemic symptoms and prompt institution of appropriate life-saving procedures, such as cardiopulmonary resuscitation (CPR) and treatment for anaphylaxis, should be paramount in the prehospital care setting.

Hot water immersion technique

Heat treatment is widely recommended as effective initial treatment for envenomations by Scorpaenidae, as well as echinoderms, stingrays, and other venomous spine injuries.

The affected limb should be immersed in water no warmer than 114ºF or 45ºC.

Be careful not to inflict thermal burns by placing an insensate limb (as a result of local anesthesia or decreased sensitivity as a result of pain) into scalding water.

Local or regional anesthesia, if available, is a suggested means of adjunctive analgesia.

Analgesia

Methods of recommended analgesia vary depending upon the reference cited and range from immersion techniques to local or regional anesthesia to parenteral analgesics.

Most references recommend that initial therapy consist of immersion in nonscalding hot water (upper limit of 114ºF or 45ºC) after removal of visible spines and sheath, in order to inactivate the thermolabile components of the venom that might otherwise cause a severe systemic reaction.

Adjunctive regional or local anesthesia offers several benefits that are not conferred by immersion techniques with analgesia. In addition to the absence of the risk of thermal injury, reliable, prompt, and prolonged analgesia allows for simultaneous debridement of the wound.

Parenteral analgesics and/or sedatives may be needed for patients who have wounds that are difficult to immerse or anesthetize, or for persons exhibiting significant anxiety reactions to the envenomation.

Wound management principles

Wound management principles include identification of foreign material, adequate debridement, tetanus prophylaxis, and appropriate referral for retained fragments that are not easily accessible in the ED.

Although the spines rarely break off into the skin, debridement of loose spines should be undertaken promptly, because retained spines continue to envenomate. Embedded structures should be pulled straight out with forceps to avoid breaking them.

Ultrasound and plain radiography may help locate retained fragments, many of which require referral for consideration of operative removal (eg, proximity to nerves, vessels, joints, weight-bearing surfaces). Retained fragments act as foreign bodies, causing inflammation and eventually becoming encapsulated into granulomata, which may lead to delayed healing and secondary infection.

Tetanus prophylaxis is indicated in all patients who have experienced traumatic marine injury and who have insufficient or uncertain immunization histories.

Severe to life-threatening systemic symptoms of envenomation most commonly result from envenomations by the Synanceia genus and only rarely result from envenomations by other genera of the Scorpaenidae family.

Stonefish antivenom

Stonefish antivenom from Australia's Commonwealth Serum Laboratories (CSL) is recommended only for predilution intramuscular usage. However, for serious envenomations, this route may not be ideal because of erratic absorption. Following dilution, a slow intravenous administration may be preferable: 1 ampule (2000 U) for every 1-2 punctures, up to 3 ampules for more than 4 punctures. It should be diluted in 50-100 mL of isotonic sodium chloride solution and run through at least 20 minutes.

As this is a hyperimmunized equine antisera, there are risks of allergic reaction and serum sickness in the recipient. Skin testing and/or pretreatment should precede administration. Rather than skin testing, Australian sources tend to recommend pretreatment with subcutaneous epinephrine and an intramuscular antihistamine, adding an intramuscular corticosteroid for known hypersensitivity.

Prevention

Most injuries and envenomations caused by Scorpaenidae result from inadvertently stepping on, carelessly handling, or harassing them.

Most Scorpaena (eg, scorpionfish) and Synanceia (eg, stonefish) species are never seen until a sting occurs because of their excellent camouflage amongst rocks or along the sea bottom. Wading in bare feet, particularly at night, should be avoided. While shoes, diving booties, gloves, and wetsuits may provide some protection, they are easily penetrated by the stout, sharp spines of stonefish, and it is best to avoid touching the sea bottom or to use a shuffling gait while wading.

Pterois (eg, lionfish) species are frequently free-swimming or hovering in small caves or crevices for protection. Do not provoke or corner these fish, as they may dart forward, resulting in an envenomation. Marine aquarists, in particular, must be cautious when cleaning their tanks or attempting to transfer captive lionfish.

Medication Summary

The goal of therapy is to control pain and prevent infections in high-risk wounds. Medical therapy is directed at providing local and systemic analgesia, wound care, and supportive therapy, including antivenom when necessary. With the exception of persons with deep puncture wounds and those who are immunocompromised, prophylactic antibiotics generally are not indicated. Once infection is established, however, prompt therapy must be instituted with emphasis on coverage for potential marine pathogens. Tetanus prophylaxis is indicated in all marine animal injuries.

A review of opioid equivalents and conversions may be found in the article Opioid Equivalents and Conversions.

This agent has clearly established efficacy for analgesia and diminution of tissue damage following envenomation by Synanceia species and may be considered for serious or nonresponding stings of other members of the Scorpaenidae family. It generally is not indicated for Pterois envenomations.

Unlike box jellyfish (Chironex) envenomations, which often require immediate antivenom administration, the clinical situation after stonefish envenomation may allow for a skin test for sensitivity to horse serum to be performed. The purpose of skin testing is to allow for adequate preparation of pretreatment, if needed, not to decide whether to administer the antivenom. This decision is based upon the clinical condition of the patient before skin testing. In addition to pretreatment, a positive skin test may warrant greater antivenom dilution in order to be safely administered.

All Australian marine antivenoms were previously made by and available from the Commonwealth Serum Laboratories, 45 Poplar Road, Parkville, Vic 3052, Australia. However, Australian venom research is now centered at the Australian Venom Research Unit, Department of Pharmacology, University of Melbourne, Parkville, Vic 3052, Australia (tel: 61-3-934447753; fax: 61-3-93482048). Stonefish antivenom is no longer available at the Health Services Department, Sea World, San Diego, CA; Sharp Cabrillo Hospital, San Diego, CA; Steinhart Aquarium, San Francisco, CA; or at Sea World, Aurora, OH. Regional poison control centers may be the most helpful sources of information. Known severe sensitivity to horse serum may prompt consideration of supportive therapy without antivenom administration.

Bupivacaine (Marcaine, Sensorcaine)

Clinical Context:
In general, any of the commonly used local anesthetics suffices; however, bupivacaine provides superior duration of anesthesia for irrigation, wound exploration, and debridement as compared to shorter-acting anesthetics. Bupivacaine increases the patient's electrical excitation threshold, which slows nerve impulse propagation and reduces the action potential; therefore, it prevents the generation and conduction of nerve impulses.

Clinical Context:
Morphine sulfate is the drug of choice for narcotic analgesia owing to its reliable and predictable effects, safety profiles, and ease of reversibility with naloxone. Morphine sulfate administered intravenously may be dosed in a number of ways and is commonly titrated until the desired effect is obtained. The analgesic route, whether oral or parenteral, is a matter of choice. With appropriate local or regional anesthesia, this medication may not be necessary.

Ciprofloxacin (Cipro)

Clinical Context:
Ciprofloxacin is a bactericidal antibiotic that inhibits bacterial DNA synthesis and, consequently, growth by inhibiting DNA-gyrase in susceptible organisms. It is indicated for pseudomonal infections and those that are due to multidrug resistant gram-negative organisms. The duration of treatment depends on the severity of infection. Generally, treatment should be continued for at least 2 days after the signs and symptoms of infection have disappeared. The usual treatment duration is 7-14 days. No controlled studies exist regarding efficacy of therapy. Several references suggest both a tetracycline and either an extended-spectrum cephalosporin (eg, ceftazidime) or an aminoglycoside.

Tetracycline (Sumycin)

Clinical Context:
Tetracycline treats susceptible bacterial infections of both gram-positive and gram-negative organisms as well as infections caused by Mycoplasma, Chlamydia, and Rickettsia species. It inhibits bacterial protein synthesis by binding with the 30S, and possibly the 50S, ribosomal subunit(s) of susceptible bacteria.

Ceftazidime (Fortaz, Ceptaz)

Clinical Context:
Ceftazidime is a third-generation cephalosporin that has a broad gram-negative spectrum, lower efficacy against gram-positive organisms, and higher efficacy against resistant organisms. By binding to one or more of the penicillin-binding proteins, it arrests bacterial cell wall synthesis and inhibits bacterial growth.

Class Summary

Antibiotics are used for outpatient treatment of early or minor wound infections and as prophylaxis for high-risk wounds (eg, deep puncture wounds, grossly contaminated wounds, persons who are chronically ill or immunocompromised). Trimethoprim/sulfamethoxazole, ciprofloxacin, tetracycline, and doxycycline are referenced as the initial oral antibiotics of choice. Others mentioned include cephalexin, amoxicillin, and amoxicillin clavulanate.

Epinephrine (EpiPen, Adrenalin)

Class Summary

Premedication is recommended by several sources because of the risks of allergic reaction and serum sickness with antivenom. In the presence of clear and severe clinical signs of stonefish envenomation, antivenom should not be withheld solely because of such considerations. The choice of specific premedication drugs is controversial but generally should include an antihistamine and epinephrine (when not contraindicated).

Hydrocortisone (Hydrocortone Phosphate, Solu-Cortef)

Clinical Context:
Prophylactic corticosteroids may prevent later serum sickness, although to date, there have been no cases reported in the literature of delayed serum sickness following any administration of marine antivenom. Hydrocortisone decreases inflammation by suppression of migration of polymorphonuclear leukocytes and reversal of increased capillary permeability.

A multitude of corticosteroid preparations are available. Methylprednisolone is widely available in the ED owing to its other uses (eg, acute asthma, spinal cord injury) and is supplied in both parenteral and oral formulations. It is therefore discussed here as a typical drug of this class.

Diphtheria-tetanus toxoid (dT)

Class Summary

Tetanus results from elaboration of an exotoxin from Clostridium tetani. A booster injection in previously immunized individuals is recommended to prevent this potentially lethal syndrome. Patients who may not have been immunized against C tetani products (eg, immigrants, the elderly) should receive tetanus immune globulin (Hyper-Tet)

Scorpionfish (genus Scorpaena) have shorter, thicker spines with larger venom glands than lionfish do, and they have a more potent sting. Courtesy Dee Scarr.

A 45-year-old diver was taking photographs in Australia at a depth of 60 feet. He suddenly noticed an excruciating pain in his left foot after resting his foot on a large stonefish. Photo courtesy John Williamson, MD and Surf Lifesaving Queensland.

Lionfish (Pterois volitans) have long, slender spines with small venom glands, and they have the least potent sting of the Scorpaenidae family. Courtesy Dee Scarr.

Scorpionfish (genus Scorpaena) have shorter, thicker spines with larger venom glands than lionfish do, and they have a more potent sting. Courtesy Dee Scarr.

Members of the genera Scorpaena, such as these scorpionfish, and Synanceia, such as the stonefish, usually are found well camouflaged on the sandy bottom of the sea or amongst rocks. Shoes or booties may provide some protection; however, it is best to avoid touching the sea bottom or to use a shuffling gait while wading. Courtesy Dee Scarr.

Members of the genus Pterois, such as this lionfish, are usually free-swimming or hovering in small caves or crevices for protection. Provoking these fish by handling or cornering them may result in a painful envenomation. Courtesy Dee Scarr.

In defense of the animals, envenomations and injury generally occur in response to a perceived threat, usually handling or stepping on the animals. Photo by Scott A Gallagher, MD.

A 45-year-old diver was taking photographs in Australia at a depth of 60 feet. He suddenly noticed an excruciating pain in his left foot after resting his foot on a large stonefish. Photo courtesy John Williamson, MD and Surf Lifesaving Queensland.

Top, Brown rockfish of the Scorpaenidae family. Lateral view of the left pelvic spine in articulation with the pelvic girdle. Middle, Anterior view of left pelvic spine (proximal portion) of the brown rockfish. Bottom, Lionfish spine.